A recent study shows that marine systems are apparently becoming gradually less able to support seabirds.
The study focused on populations that scientists had monitored at least five times between 1950 and 2010, which accounted for 19 percent of the world’s seabird population, encompassing 162 species.
Despite many threats, there are a number of conservation measures that can be taken to protect seabird colonies.
Since seabirds rely on healthy oceans to feed and thrive, scientists consider them excellent indicators of the marine ecosystem’s health. But a recent study found that global seabird populations appear to be rapidly dwindling, a possible sign of overall marine ecosystem decline.
Seabirds “travel far and wide to forage… and, unlike most marine species, return to terrestrial colonies where their population sizes tell us a lot about the health of the world’s oceans,” Michelle Paleczny, a zoologist at the University of British Columbia and the lead author of the new paper, told mongabay.com.
The present study, published in the journal PLOS ONE, showed that marine systems are apparently becoming gradually less able to support seabirds. Researchers collected data on seabird population sizes from a variety of primary sources, including books, academic journals, and unpublished reports. They focused on populations that scientists had monitored at least five times between 1950 and 2010, which accounted for 19 percent of the world’s seabird population, encompassing 162 species.
The researchers then tracked the birds’ population sizes over time by applying a modeling system to their database that extrapolated missing population data and estimated errors in the collected data. This model allowed the researchers to obtain a comprehensive look at population trends from 1950 to 2010.
The researchers found that during that period the monitored seabird populations declined by 69.7 percent.
Despite the drastic decline observed overall in the global seabird population, the researchers found that a majority of seabird populations actually increased in numbers. The authors explained in the paper the reason behind this discrepancy. “While many small populations have been observed to increase, these increases are swamped by large decreases in fewer, but larger populations.”
While these results come from data gathered on just 19 percent of the world’s seabirds, they may well apply to all seabirds. “Investigation of how well our subsample represents the global population revealed no strong bias towards particular taxa, marine regions or declining populations. Half of all seabird species were represented and thirteen of fourteen families were represented,” the authors write in the paper.
Their findings corroborate the only other global study of seabird population trends. That study, published in 2012, found that one-third of seabird species are threatened, at least half are in decline, and at least four species are known to be extinct.
“We were not surprised to observe an overall decline in seabirds, given the many threats that they face,” Paleczny said.
Threats to seabirds are increasing over time. According to Paleczny’s study, one big game-changer for seabirds over the last century has been the industrialization of fishing, which has depleted seabirds’ food sources. Other threats include entanglement in fishing gear and oceanic pollution.
But the danger for seabirds doesn’t end at sea. When birds return to land from oceanic foraging, they find that their habitats are being developed and that invasive, often predatory, species are being introduced to their homes.
Despite many threats, there are a number of conservation measures that can be taken to protect seabird colonies and, hopefully, allow populations to grow — and many of them have the added benefit of improving the wellbeing not only of seabirds, but of marine ecosystems as a whole. These include protecting terrestrial habitats that seabirds use for nesting and breeding, as well as eliminating invasive species in these areas, especially those that prey on seabirds.
A goal of this study was to communicate to people the impact that problems like pollution, overfishing, and invasive species are having on marine ecosystems, Paleczny said.
“[B]y summarizing the overall trend in all available seabird data, we get a big picture perspective, and can easily communicate to people and marine ecosystem managers that seabirds and marine ecosystems are very impacted by marine threats around the world,” she said.
Paleczny M., Hammill E., Karpouzi V., Pauly D. (2015.) Population Trend of the World’s Monitored Seabirds, 1950-2010. PLOS ONE 10(6): e0129342. doi:10.1371/journal.pone.0129342
Croxall, J.P., Butchart, S.H.M., Lascelles, B., Stattersfield, A.J., Sullivan, B., Symes, A. Taylor, P. (2012). Seabird conservation status, threats and priority actions: a global assessment. Bird Conservation International 22(1): 1-34.